Because there is no need or benefit. The interface is not a bottleneck. Optical drives, by their nature, are relatively slow - even USB 2.0 is more than fast enough for an optical drive. A thunderbolt interface would do nothing but add expense, as an optical drive could
never be fast enough to utilize it. There would be zero benefit.

Yes, but you'll need one of the USB-C adapters that has a USB 3.0 port. And the SuperDrive must be plugged directly into the USB 3.0 port on the adapter, not connected through a hub, so no other USB devices can be used while you're using the USB SuperDrive.

Yes, I have successfully used this drive with my 2016 MacBook. You will need a USB to USB-C converter, however, as this drive is USB. Its worth mentioning I was successful using an Apple HDMI Multi Adaptor, I wouldn't be able to say with 100% certainty that this would work with other non Apple brand adapters.